1. Field of the Invention
The present invention relates to spacer blocks positioned between aluminum ingots in preheat furnaces, more particularly, to spacer blocks produced from a ceramic material having resistance to high temperature heat and high compressive strength at room temperature and up to use temperatures of about 1160xc2x0 F.
2. Prior Art
Heating of the aluminum ingots is a well-established practice for achieving desired properties in the ingot and to render the ingot sufficiently malleable for reduction in thermo-mechanical processes. During the preheating step, aluminum ingots are heated to temperatures below the melting point of the aluminum alloy. Preheating serves to control the metallurgical properties of the ingot, reduce cracking, and reduce the forces needed to further process the ingot. Typically, up to six ingots are stacked vertically in a preheat furnace at one time. To prevent the ingots from sticking to one another and to allow hot gases to circulate between the ingots for faster heatup and uniform exposure to the furnace atmosphere, spacer blocks are positioned between the stacked ingots to maintain a gap between the ingots.
Conventional spacer blocks are solid blocks of an aluminum alloy (which may be the same as or different from the alloy of the ingot supported thereby) sized about 1-4 inchesxc3x972-6 inchesxc3x976-24 inches and often weighing over 10 pounds. A single operator may handle 400 to 500 spacer blocks per shift. Such repeated handling of conventional spacer blocks could cause ergonomic problems for operators of preheat furnaces.
Additional drawbacks to conventional spacer blocks relate to their composition. When heated in a furnace, the metal of the ingot as well as the metal of the spacer blocks soften. In addition, oxide layers grow and volatile metals, such as magnesium and lithium, migrate to the surfaces of the spacer blocks and the ingots. The migrated metals cause the spacer blocks and the ingots to adhere to one another. Deformation and adhesion of the spacer blocks to the ingots is particularly problematic for the ingots at the bottom of the stack where the load is the greatest. When the preheat cycle is complete, a crane is used to remove an ingot from the stack and position the ingot at the beginning of a hot line rolling mill, reversing mill, or the like. An operator must remove any spacer blocks stuck to the ingot. Occasionally, the spacer block can be removed from the ingot by simple hand pressure. However, often times the spacer block is so tightly adhered to the ingot that it must be knocked off with a large hammer or an axe. Occasionally, a forklift or the like must be used to loosen the adhered spacer block from the surface of the ingot. Removing spacer blocks from a heated ingot by an operator exposes an operator to risk of injury from the equipment for handling the spacer block and the heat of the spacer block.
An additional problem with sticking of spacer blocks to ingot is the marks, which are typically left on an ingot upon removal of the spacer block. Spacer blocks often produce defects in the surface of the ingot. When an ingot having such a defect is subsequently rolled, the defect becomes a streak of a surface imperfection in the rolled product. For many applications of the rolled product, such defects are unacceptable in the marketplace.
Another drawback to the aluminum spacer blocks is the tendency of the various aluminum alloys of the blocks to creep at high temperatures. At temperatures of about 900-1140xc2x0 F., spacer blocks having an initial dimension of 3 inchxc3x973 inchxc3x9712 inch become deformed into dimensions of about 2.5 inchxc3x973.5 inchxc3x9712.5 inch. Not all spacer blocks in a stack of ingots are always deformed similarly. Hence, in a set of spacer blocks used with a stack of ingots, the individual spacer blocks may have differing dimensions. Variable dimensions in the spacer blocks can aggravate sticking of the spacer blocks to the ingots. For example, when six spacer blocks are used for an ingot and two of the spacer blocks do not touch the ingot because they have been deformed, only four of the spacer blocks contact the ingot and support the entire load. In this situation, the load per unit area borne by the four spacer blocks contacting the ingot increases by about 33%. At such higher loads, the adhesion between the spacer blocks and the ingots is aggravated.
High temperature creep of aluminum spacer blocks is also a problem in preheat furnaces operated at higher temperatures, e.g., at or above about 1120xc2x0 F. It has become common practice in those circumstances to position the spacer blocks between the ingots so that a portion of the spacer block extends out between the ingots. During the preheat cycle, the portion of the spacer block which is sandwiched between the ingots becomes flattened to a thickness of about xc2xd inch while the remaining portion of the spacer block which did not support the ingot retains its original width and height (3 inchxc3x973 inch). In order to reuse those spacer blocks, which have been partially flattened, operators turn the spacer blocks around and position the unflattened portions of the spacer blocks between ingots. This results in the entire spacer block being flattened into a thickness of about xc2xd. When the spacer block between the ingots is reduced to about xc2xd inch, airflow between the ingots is greatly reduced which results in uneven heating, extended cycle times, and insufficient exposure of the ingot surfaces to the furnace atmosphere.
Accordingly, a need remains for a spacer block for use in aluminum ingot preheat furnaces which is lightweight, does not stick to the ingot surfaces, and retains its shape during an ingot preheat cycle.
This need is met by the spacer member of the present invention, which may be used for supporting an aluminum alloy product subjected to a heat treatment. The spacer member includes a metal housing with a core of a ceramic material and having a surface, which is configured to support an aluminum alloy ingot in a furnace. The metal housing is preferably in the form of a metal tube, which may be an extruded tube, roll formed tube or a welded tube. The tube is capped at each end. The ceramic material contained within the metal tube is stable at high temperatures (e.g., up to about 2000xc2x0 F.). The exterior of the support member of the present invention may be coated with a material to prevent sticking of the spacer member to an ingot in a preheat furnace. The spacer member of the present invention has dimensions preferably the similar to those of conventional aluminum spacer blocks, e.g. about 3 inchxc3x973 inchxc3x9712 inch but weighs less than 10 pounds.
The spacer member of the present invention may be produced by providing a metal housing, such as a tube capped at one end, filling the housing with a ceramic material and enclosing the ceramic material within the housing by capping the other end of the tube. The housing may then be coated with a nonstick material to prevent the spacer member from sticking to an ingot in a preheat furnace.
A complete understanding of the invention will be obtained from the following description when taken in connection with the accompanying drawing figures wherein like reference characters identify like parts throughout.